This invention relates in general to concrete paving, and more particularly to a machine and process for laying slabs of concrete mix against previously laid slabs while the concrete mix of the previously poured slabs is still plastic.
Concrete, although being a highly durable substance, is not widely used for paving large expanses such as parking areas. Instead, most large parking areas are paved with asphalt, primarily because asphalt is easier to apply. In this regard, the asphalt is usually laid over a large expanse in strips, and no difficulty is encountered laying one strip adjacent to a previously laid strip, even though the time between depositing the material of the two strips is only a few minutes. However, asphalt will not support the weight that can be supported by fully cured concrete, and furthermore it will deteriorate when subjected to leaking motor oil and other petroleum products. Also, the significant increase in the cost of crude oil has elevated the cost of asphalt paving to almost as much as that of concrete paving.
Originally concrete paving required the erection of shallow forms over the area to be paved, but this is a time consuming procedure involving much manual labor. Moreover, it proved difficult construct one form adjacent to another so the area was usually paved in strips, with each strip initially being confined by a form and being separated from the adjacent strip by an unpaved strip of equal width. After the forms were removed, the unpaved voids between the strips could be poured to complete the area, but the concrete in the paved strips had to cure sufficiently to gain enough strength to support the concrete carrying vehicles. This usually required at least several days.
This traditional approach has to a measure been rendered obsolete by slip-forming machines which in effect extrude concrete onto the ground in a wide variety of configurations depending on the mule or slip form that is used. For example, some slip forms are suitable for gutters, some for highway barrier walls, and some for curbs. Others are configured for laying sidewalks or paving, but again whenever a large expanse is to be paved, the slip-formed paving must be laid in parallel strips with spaces between adjacent strips. This significantly extends the time for completing the work, since the unpaved intermediate areas between adjacent strips or slabs cannot be paved until the paved regions have cured enough to hold cement-carrying vehicles. Heretofore, it has been impossible to lay a slip-formed slab alongside a previously laid slip-formed slab that is still plastic. The difficulty resides primarily in keeping the slabs at the same elevation and also in steering the slip-forming equipment so that it keeps the slab that it is laying against the previously laid plastic slab. These difficulties exist even though the slip-forming machines are provided with very sensitive control equipment and quite a few adjustments for both steering and elevation.
Thus, present methods of laying concrete paving, even when slip-forming machinery is employed, are not nearly as easy or as rapid as the methods currently used to lay asphalt paving, and this derives primarily from the fact that a slab of concrete mix cannot be laid against a previously laid slab of concrete mix that is still plastic, whereas a strip of asphalt can be laid against a still plastic strip of asphalt.